The present invention relates to a semiconductor integrated circuit device and, for example, relates to a technique effective to a semiconductor integrated circuit device suitably used for a power supply device.
In recent years, various electronic devices such as cellular phones and digital home appliances are becoming smaller, lighter, and multifunctional. For power supply devices for driving those devices, demands for higher reliability, miniaturization, and higher efficiency are increasing. Since a switching power supply device has advantages such as small size and high efficiency, it is widely used as a DC power supply of various electronic devices.
Two kinds of the control methods often used for a switching power supply device are a linear control method and a non-linear control method. A representative linear control method is a PWM (Pulse Width Modulation) control method which stabilizes output voltage by adjusting the timing of turning on/off a switching element by using a PWM signal of fixed frequency. On the other hand, a representative non-linear control method is a hysteretic control method in which a deviation of output voltage from a predetermined range (hysteresis width) is detected by a hysteresis comparator, and an output of the comparator controls the on/off state of the switching element. Since the hysteretic control method has an advantage that response speed is higher than that of the PWM control method, attention is being paid to the hysteretic control method.
As the hysteretic control method, an analog control power supply device realized by analog circuits is common. However, in recent years, miniaturization of a power supply device is strongly demanded, so that development of an analog control power supply device is being advanced rapidly. An analog control power supply device performs control by using analog circuits such as an amplifier, a capacitor, and a resistor. On the other hand, a digital control power supply device digitally performs control by using an AD converter and a digital controller.
In a digital control power supply device, since a part of a control circuit is realized by digital process, parts can be reduced, and miniaturization can be expected. In recent years, a plurality of methods each realizing a digital control power supply device having high response speed by using the hysteretic control method are proposed (Non-patent literatures 1 and 2).
A digital control power supply device (non-patent literature 1) will be described. By measuring switching on and off times of the previous switching period and switching cycles, the tilt of inductor current change in the switching on and off periods is obtained as a first measurement result. A sampled inductor current value is obtained as a second measurement result. From the first and second measurement results, time reaching a control threshold is predicted. The digital control power supply device does not require a high-speed AD converter and a high-speed digital controller and realizes low power consumption.
Another digital control power supply device (non-patent literature 2) will now be described. Inductor current is sampled at two points during a switching on period, and is sampled at two points also in a switching off period. By the sampling at four points, the tilt of the inductor current change is obtained. Together with the sampled inductor current values, time reaching the control threshold is predicted. The digital control power supply device does not require a high-speed AD converter and a high-speed digital controller and realizes low power consumption.
Prior art literatures were examined on the basis of the present invention and the following related arts were found.
Japanese Unexamined Patent Publication No. 2008-125286 (patent literature 1) discloses a switching power supply which predicts a deviation of the following cycle from a deviation corresponding to the voltage value between reference voltage and output voltage and performs PWM control on the basis of the predicted deviation.
Japanese Unexamined Patent Publication No. 2011-166959 (patent literature 2) discloses a DC/DC converter of PWM control realizing improved response of power supply control by increasing the speed of PID computation by making the PID computation progressed halfway on the basis of an error signal in a plurality of past cycles.